The Northern Expressway project is a joint initiative by the Federal and South Australian governments under the Australian Government's Nation Building Program. The AUD$564 million project is the largest road construction project undertaken in the state since the 1960s.

The 23 kilometre expressway includes numerous bridges and interchanges, as well as a shared pedestrian and cyclist path.

In all, two hundred tonnes of XLERPLATE® steel were used to construct the Snake Wall, which will become an architectural and cultural landmark.

The Snake Wall winds its way along the northern end of the four lane expressway.

WR350 grade XLERPLATE® steel was specifically selected for the Snake Wall because, as Rick Modzelewski, Manager ID Fabrication, of the company which fabricated the steel explained, "Its weathering capabilities, unlike normal mild steel, contain alloying elements. This causes it to weather to a uniform patina in its natural state, due to the formation of an impervious oxide, after which no further corrosion takes place."

Dallas Keane is a Construction Manager with York Civil – an engineering, construction and project management company which partnered with civil contractor Fulton Hogan to construct the Northern Expressway.

"The Snake Wall project was unusual for distinct reasons," Dallas said. "This huge project required the XLERPLATE® steel used to undergo significant profile cutting and have a finished curved profile. This required a combination of rolling panels for large curves and bending panels on site for the smaller curves."

Dallas said the team faced a number of engineering challenges. "Designing the supports for the steel without limiting the visual effect of semitransparent steel, which we created with holes in the steelwork, and the continuity of the overall effect between panels was a real challenge," Dallas said.

"We also had to find a solution to creating the varying curved radii of the walls, without rolling each individual panel. The solution was to bend Snake Wall panels on site, where possible, by the use of temporary anchors," he explained.

Fabrication and profiling

Gordon Smith, Manager of Adelaide Profile Services (APS), which profiled and supplied the steel, said XLERPLATE® steel was used because of the availability of the product from a local manufacturer, consistency and guaranteed supply on a tight lead time, the desired grade being available and the product's quality guarantee.

APS supplied the following XLERPLATE® steel Snake Wall components:

  • 190 wall panels (cut with profile shapes replicating snake scales)
  • 380 bases for the steel wall
  • 380 fins (tall uprights that are supports for the vertical steel plate)
  • 380 gussets (on the bottom part of the wall, used as a strengthening device welded to fins and base).

Gordon emphasised that, "Producing nearly 200 of anything is a lot! The wall is five metres high and the panels are 2.4 metres wide. The snake skin pattern runs the 500 metre length." Elements that APS and ID Welding & Fabrication worked on included:

  • plasma cutting (including the unique snake skin elements)
  • the bevelling and drilling of the fins
  • welding the fins and gussets to the bases
  • bolting the components together.

Colour retention, an important consideration in a job like this where aesthetics are critical, across the welds was achieved by appropriate electrode selection.

Teamwork and trialling

In a project such as this, the importance of teamwork between engineers, profiler, fabricator, distributor and supplier was emphasised. "The integration between the designers, architects and construction team went very well," said Dallas.

"This led to a clear understanding of each party's goals and limitations, while creating the best outcome practicable. This was seen in the ongoing project workshops to develop the concept and the readiness of each party to understand each other's requirements," said Dallas.

"The involvement of the fabrication team, including the profile cutting contractor, allowed a direct input into what was a very satisfying outcome. We all worked together to ensure the program was maintained and the outcome was the 'best for project'."

York Civil instigated a mock setup trial for the XLERPLATE® steel prior to the project going ahead. This enabled the team to accurately assess what was reasonable to bend, using the natural flexibility in the steel, and what required cold rolling," Dallas continued.

Early development of the final solution and workshopping options enabled work to be completed without excessive program pressure. The early ordering of the materials prior to final artistic shop drawings being approved helped in material supply not becoming a critical issue.

Innovation with steel

The innovative approach of the project was not limited to the use of the weathering XLERPLATE® steel or its aesthetically pleasing application. Two further innovative dimensions had sustainability aspects inherent to them.

Firstly, the thickness of the steel was minimised by the introduction of the support fins. This meant less steel needed to be used, which also reduced the cost of the steel whilst maintaining the overall integrity of the wall. And secondly, using weathering steel means ongoing maintenance and protective treatments (including paint) are not required.

This was a project, however, that had innovation inherent at its very core due to the manner in which it integrated important cultural and social elements from the local community.

Various characteristics of the project prompted the large scale sculptural response of the Snake Wall, which celebrates the entry/exit point to the northern Adelaide plains. During consultation with the local Kaurna Aboriginal community, discussions focused around land at the northern end of the Northern Expressway being known as 'snake country'; whilst to the south it was known as 'dog country'.

Artist Robert Owen developed the Snake Wall installation to acknowledge Aboriginal stories of place, as well as the local fauna of the region.

Steel was selected as the construction material to reference the industrial history of nearby Gawler's former steel ship building industry and machinery manufacturing. The patterning of the cut steel panels was developed from scans of the skin of a Redbellied Black Snake. It represents a lace like tracing in an ephemeral landscape. The design and material also references masculine (steel) and feminine (lace), nature/culture, native fauna species and Aboriginal history.

A native grassland will be planted in front of the Snake Wall to make it appear as if the snake is slithering its way across the landscape. At night, the wall will be flood lit from behind with red LED lights, creating a striking effect.